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       bhost - LAM boot schema (host file) format

       # comments
       <machine> [cpu=<cpucount>] [user=<userid>]
       <machine> [cpu=<cpucount>] [user=<userid>]

       A  boot	schema	describes  the machines that will combine to form a multicomputer running
       LAM.  It is used by recon(1) to verify initial conditions for running LAM,  by  lamboot(1)
       to start LAM, and by lamhalt(1) to terminate LAM (note that wipe(1) has been deprecated by
       the lamhalt(1) command).

       The particular syntax of a LAM boot schema is sometimes called the "host file" syntax.  It
       is  line  oriented.  One line indicates the name of a machine, typically the full Internet
       domain name, an optional number of CPUs available on  that  machine,  and  optionally  the
       userid with which to access it.

       Common  boot  schema  for a particular site may be created by the system administrator and
       placed in the installation directory under etc/.  They typically  start	with  the  prefix
       bhost.	Individual users usually create their own boot schema, especially if the configu-
       rations are simple.

       Here is an example three node boot schema:

       # example LAM host file
       beowulf1.nd.edu cpu=2
       somewhere.else.college.edu user=guest

       Note that the "guest" ID is significant, since the user has an alternate login ID on some-
       where.else.college.edu.	 Additionally  note  that beowulf1 has a CPU count of 2 listed (a
       CPU count of 1 is assumed if  it  is  not  given).   This  value  is  used  by  mpirun(1),
       MPI_Comm_spawn(2), and MPI_Comm_spawn_multiple(2) for the "C" (or CPU) notation that spec-
       ifies how many ranks to start.  This is particularly useful for running on SMP machines.

       beowulf2 is listed twice, but has no specific CPU count listed.	In this  case,	LAM  will
       keep a running tally of the total number of CPUs for that host.	Hence, LAM will calculate
       that beowulf2 has two CPUs available for use.  Calculating the number of CPUs by  counting
       occurances  of  a  hostname is useful in a batch environment where a hostfile may list the
       same hostname multiple times, indicating that the batch scheduler has  allocated  multiple
       CPUs for a single job (e.g., PBS operates this way).

       For  the  above-mentioned schema, the command "mpirun C foo" would start five instances of
       the foo program; two on beowulf1, two on beowulf2, and one on somewhere.else.

       $LAMHOME/etc/bhost.def		 default boot schema file

       lamboot(1),   lamhalt(1),   mpirun(1),	MPI_Comm_spawn(1),    MPI_Comm_spawn_multiple(1),
       recon(1), wipe(1)

LAM 6.5.8				  November, 2002				 BHOST(5)
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